The Long Term 2 Enhanced Surface Water Treatment Rule ("LT2ESWTR" or simply "LT2") is a 2006 regulation promulgated by the United States Environmental Protection Agency (EPA) pursuant to the Safe Drinking Water Act.
[1] EPA began drafting the LT2 rule following the 1993 Milwaukee Cryptosporidiosis outbreak, in which it is believed that municipal sewage infected with cryptosporidium was accidentally discharged into the city of Milwaukee, Wisconsin's drinking water.
[2] The LT2 rule was criticized for mandating costly public works projects (such as coverage of open-air reservoirs) that may be unnecessary[3] and/or unlikely to address the kind of problem that was responsible for the Milwaukee incident.
William R. MacKenzie, M.D., a Centers for Disease Control epidemiologist who served as the Epidemic Intelligence Officer on the Milwaukee case, stated, "Standards for water treatment facilities were about to be implemented throughout the nation; but even those would not have stopped the Milwaukee outbreak.
In a 2017 Federal Register notice, EPA stated that it "did not identify new information related to potentially revising" the regulatory requirements for cryptosporidium and other listed pathogens, and requested additional public comments.